As is well known in the medical field, sleep apnea is a disorder that affects more than 12 million people in the United States alone. It takes its name from the Greek word apnea, which means “without breath.” People with sleep apnea literally stop breathing repeatedly during their sleep, often for a minute or longer, and as many as hundreds of times during a single night.
Sleep apnea is known to be caused by either complete obstruction of the airway (obstructive apnea) or partial obstruction (obstructive hypopnea), both of which can cause the person suffering from such sleep apnea to wake up, temporarily, in order to breathe. There are three types of sleep apnea—obstructive, central, and mixed. Of these, obstructive sleep apnea (OSA) is the most common. OSA occurs in approximately 2 percent of women and 4 percent of men over the age of 35.
The exact cause of OSA remains unclear. The site of obstruction in most patients is the soft palate, extending to the region at the base of the tongue. There are no rigid structures, such as cartilage or bone, in this area to hold the airway open. During the day, muscles in the region keep the passage wide open. But as a person with OSA falls asleep, these muscles relax to a point where the airway collapses and breathing becomes impossible. When breathing stops, the sleeper partially awakens, involuntarily tenses the muscles in the region to open the airway in order to breathe, and falls back asleep. The arousal from sleep usually lasts only a few seconds, but these brief arousals disrupt continuous sleep and prevent the person from reaching the deep stages of slumber, such as rapid eye movement (REM) sleep, which the body needs in order to rest and replenish its strength. Even though normal breathing is restored when the person awakens briefly, the cycle is repeated throughout the night. Typically, the frequency of waking episodes is somewhere between 10 and 60, although a person with severe OSA may have more than 100 waking episodes in a single night.
Positive airway pressure has been demonstrated to be a very effective treatment for obstructive sleep apnea. It has three forms: continuous positive airway pressure (CPAP), autotitration, and bi-level positive airway pressure (BIPAP). While positive airway pressure is usually easier to tolerate at lower pressures, every patient requires a different pressure. In order to determine each individual patient's optimum airway pressure, it is necessary to titrate the pressure to each individual patient during a polysomnogram. A polysomnogram will show not only when the respiratory events have ceased, but also when the arousals from the respiratory events occur.
CPAP, the most common of the three therapy modes, is usually administered at bedtime through a facial mask held in place by straps around the patient's head. The mask is connected by a tube to a small air compressor about the size of a shoe box. The CPAP machine sends air under pressure through the tube into the mask, where, assuming a good seal with the patient's face, it applies a positive air pressure to the upper airways. This positive air pressure essentially “splints” the upper airway open and keeps it from collapsing.
Approximately 55 percent of patients who use CPAP do so on a nightly basis for more than four hours. The advantages of CPAP are that it is very safe and completely reversible. Generally, the treatment is well tolerated; however, it suffers from the disadvantage that it requires active participation every night; that is, the patient must put it on for it to work. If the mask is ill-fitting or causes unwanted side effects, compliance will not be maintained.
Nasal CPAP Masks on the market today fall into one of three design categories. They are either nasal masks, full face masks (i.e., those which cover the mouth and nose) or nasal pillows. The vast majority of CPAP masks that are currently on the market are comprised of a rigid plastic frame buffered by an elastomeric, rubbery “cushion” that makes the actual contact with the patient's face. These masks are sealed to the patient's face by tightening straps that hold the mask to the patient's head to increase mechanical pressure against and into the skin of the face. The skin and tissue of the patient's face is compressed by the mask, which forms a “gasket” that creates a seal and keeps the air pressure inside the mask elevated. Unfortunately, aside from being uncomfortable, a disadvantage to this approach is that the mechanical pressure applied to the patient's skin often exceeds the perfusion pressure in the tissue under the skin. Consequently blood flow to the tissue is diminished or cut off entirely. This leads to pain and can ultimately cause pressure sores on the patient's face. Additionally, it has been discovered that some of the masks, which use a silicone or a polyurethane gel to touch the face, have caused allergic reactions in some users.
These problems were largely overcome by the soft cloth mask disclosed in U.S. patent application Ser. No. 12/070,463 (the “'463 application”). The '463 application disclosed a nasal CPAP mask that was entirely comprised of a non-rigid, compliant material that had no fixed shaped unless breathable gas at positive pressure was flowing into it. While the nasal mask of the '463 application remedied many of the drawbacks with then-existing masks, it still occasionally suffered from air leakage at the interface between the patient's nose and the mask, due largely to the manner in which the nasal interface was constructed. The air leakage was a problem for many reasons, including, reduction of positive pressure applied to the patient's airway, dry eyes from air blowing into them, disruption of sleep of bed partner caused by both blowing jets of air and noise associated therewith.
The problems with air leakage in masks constructed in accordance with the '463 application were largely remedied by the introduction of the nasal interface disclosed in U.S. patent application Ser. No. 12/905,404 (the “'404 application”); however, there remained a small population of mask users who still experienced some difficulty in getting the mask to fit properly. When the previously disclosed mask was tightened on a user's face using the straps, the compliant material was occasionally stretched in a way that provided a less than optimal fit. Additionally, the mask of the '463 and '404 applications had a swivel connector that was affixed to the mask with tape, which made repeated cleaning of the mask challenging as re-taping the swivel to the inside of the mask required dexterity not possessed by all. Still further, the mask of the '463 and '404 applications included a headgear that connected to the mask from the top of the head, down across the forehead and between the eyes and to the bridge of the nose, which sometimes got in the way while the user was watching TV or reading a book. The mask of the '463 and '404 applications also included a swivel connector that allowed the air hose to rotate 360-degrees axially, but did not provide any angular freedom in that it only permitted the air hose to be directed downward away from the mask instead of providing the option to be directed sideways or upward toward the hairline of the user, for example. The present invention resolves the aforementioned problems.